Digital signal compression (sometimes referred to as video coding or video encoding) is widely used in many multimedia applications and devices. Digital signal compression using a coder/decoder (codec) allows streaming media, such as audio or video signals to be transmitted over the Internet or stored on compact discs. A number of different standards of digital video compression have emerged, including H.261, H.263; DV; MPEG-1, MPEG-2, MPEG-4, VC1; AVC (H.264), and HEVC (H.265). These standards, as well as other video compression technologies, seek to efficiently represent a video frame picture by eliminating the spatial and temporal redundancies in the picture and among successive pictures. Through the use of such compression standards, video contents can be carried in highly compressed video bit streams, and thus efficiently stored in disks or transmitted over networks.
Encoding the same video content at multiple resolutions is often necessary for video streaming over the network and for targeting different decoding hardware with different computational capabilities. For example, it is sometimes necessary to encode video with multiple resolutions due to bandwidth limitations and due to recent advances in the capabilities of video encoding and decoding hardware. With the growing popularity of 4K displays (picture width of 3840 to 4096 pixels), the demand for higher resolution video content has increased. The storage required for 4K video is much higher than for 1080p HD video. In some cases, storing both lower and higher resolution versions of the same video content might be necessary, e.g., for display on different hardware. Having both HD and 4K resolution video streams on a Blu-Ray disc could allow a lower powered video player to display the HD content and a more powerful video player to display the 4K content. However, due to storage limits on physical discs, it might not be possible to fit both resolutions on a single disc. One approach to addressing this issue is to produce both low resolution and high resolution discs for the same content. For video streaming over a network, the higher resolution video could be displayed when the bandwidth is high and the lower resolution could be displayed during network congestion. Fewer bits are needed to transmit lower resolution encoded video (e.g., 1080p HD video) than higher resolution (e.g., 4K) video.
Another approach is to encode the low resolution video and to up-sample it when presenting it on the higher resolution hardware. However, the video quality suffers when the up-sampled low resolution video is played on the high resolution hardware. Yet another approach is to store just the high resolution encoded video on disk. Unfortunately, low powered hardware might have to skip frames because it's not powerful enough to maintain the desired frame rate for the higher resolution video.
Having multiple discs increases the production costs, while storing only one resolution of the video on the disc does not allow the best experience for either the lower powered or the higher powered player. If only the lower resolution video is stored on the disc, the displayed picture will require up-sampling on higher resolution displays. The picture quality of up-sampled video content will be lower than that of content that is originally of higher resolution. If only the higher resolution video is stored on the disc, lower powered devices may not be able to display the content at the original frame rate, and may have to drop frames or lower the frame rate. This too results in a reduced user enjoyment.
While an extension to the Advanced Video Coding (AVC) standard known as Scalable Video Coding (SVC) allows efficient compression for multiple resolutions, the number of devices that support this extension is much lower compared to those that do not. As a result, the common approach to handling multiple resolutions is to resize the video content to multiple resolutions before encoding, and generating separate bitstreams for each resolution that could be decoded independently of each other.
It is within this context that aspects of the present disclosure arise.